Smokeless powder containing acrylic polymers



United States Patent 3,149,012 SMUKELESS PQWDER CONTAINING ACRYLEC PQLYWRS Raiph F. Preckel, Cumberland, Md, assignor, by rnesne assignments, tothe United tates of America as represented by the Secretary of the Navy No Drawing. Filed Nov. 14, 1955, Ser. No. 546,763 1.1 Claims. (Cl. 1149-98) This invention relates to the manufacture of smokeless powder and more particularly to an improved solvent process for manufacturing smokeless powder and the improved products obtained therefrom.

Currently, smokeless powder is prepared either by the solven process, by solventless extrusion, or by a casting procedure. In the solvent process, nitrocellulose is dissolved in or colloided by the addition thereto of a volatile solvent such as acetone, ether-alcohol, acetonealcohol, and the like, and by mixing the nitrocellulose and solvent until a viscous or doughy mass is obtained. This mass is then granulated by extrusion and cutting or other suitable means and the volatile solvent is removed as completely as possible. While this process has been a standard means for producing smokeless powder, particularly in small granulations, it has always been recognized that the amount of time necessary to extract the volatile solvent from the grains is undesirably great. It is an accepted fact that the volatile solvent, because of its great affinity for nitrocellulose, is never completely removed from the grains in any practical drying time and that even in small granulations residual solvent migration results in changes in ballistics. Because of the great difiiculty in removing the volatile solvent, the process is not used where a powder web of greater than 0.5 inch is desired.

Because of the limitations of the currently known solvent process, the solventless extrusion techniques were developed. In the conventional solventless extrusion method, the desired powder ingredients are mixed in the presence of Water. The resulting paste or slurry is then dried to the desired moisture content and the resulting mass is rolled on hot rolls to obtain a colloided sheet. This sheet is then extruded or flaked into the desired granulation. While it has been necessary to employ this process in place of the solven process where a powder web of greater than about 0.5 inch is desired, it has long been recognized that the solventless extrusion process leaves much to be desired from the viewpoint of a facile manufacturing operation. For example, in solventless extrusion techinques poor quality is occasionally caused in the extruded grains by air which is trapped within the charge prior to extrusion. Moreover, the large amount of manual handling involved makes the solventless extrusion process relatively expensive.

When even larger powder grains with even thicker webs became desirable for use in rockets and in JATO units, it was recognized that due to the massive nature of the extrusion presses which would be necessary to produce such large grains, including handling and preforming for the press charge, even the solventless extrusion process was unsatisfactory. As a result, several casting techniques have been developed in which small granules, usually manufactured by the solvent process, are introduced into a mold together with the desired explosive and nonexplosive nonvolatile plasticizers and agrain of the desired size is cast by the solvation of the granules by the plasticizer. However, in order to produce a cast grain in this manner, it is necessary to accept the disadvantages of either the solvent and solventless extrusion processes in the production of the base grain to be used in the casting operation.

Now in accordance with the present invention, a process has been discovered which permits manufacturers of smokeless powder to take advantage of the desirable characteristics of the solven process and yet avoid the presence of volatile constituents in the finished product. Furthermore, the process leads to a new article of manufacture comprising granulated smokeless powder substantially free of volatile constituents.

Generally described, the present invention is a process for manufacturing smokeless powder which comprises forming a uniform doughy mass containing from 15-50% of nitrocellulose, from 1560% of liquid explosive nitric ester and from 530% of at least one catalyzed liquid polymerizable material of the group consisting of the methyl, ethyl, propyl, butyl, and isobutyl esters, and the nitriles of acrylic and methacrylic acids, extruding the mass and cutting-into the desired granulation, and curing the grains at a temperature of above 20 C. and below the ignition point of any of the ingredients to form a polymerized product substantially free from volatile constituents. The present invention further contemplates the novel products thus produced.

Having generally described the invention, the following examples are given to illustrate specific embodiments of the invention.

In Table 1, data are given which compare the performance in cal. .30 cartridges of a standard single-base powder with a powder of comparable potential formulated and produced in accordance with the invention. The powders had the following formulations:

Standard Invention Nitrocellulose (13.25 N) 85.0 38.0 Dinitrotoluene i f 10.0;; Dibutylphthalate. 5.0% Drphenylamine..- 1.0% (Added) Ethyl Centralite 1.0%. Nitroglynerin 40.0%. Solvent 70 parts, Ether] 21.0% (Polymer- Alcohol /35. izab1ec0ntains 0.5-1.0%) (eat).

. 3 A A powders were loaded 1n cal. .30 components and fired In Table 3, data are presented which compare the perwlth the followlng results: formance 1n cal. .30 cartridges of a standard trlple base Table 1 Cut Charge Mean Mean Example Solvent Grain Die.., Weight Air N0. Veloo- Pres- Catalyst,

Pin Die. (gr.) Space Shots ity, sure, percent ftJsec. p.s.i.

Standard Ac/alo 16 52.0 -0. 02 5 2,346 43,700

0053-. 015 1 MMA 16 48.0 -0. 03 5 2,123 44, 000 (A) 1.0 0. 053-. 015

2 MMA 16 55.0 0.00 5 2,264 44,100 (A) 1.0

0. 040-. 010 3 MA 32 31.0 74 5 2,351 41,600 (A) 0.5 0. 040-. 010

4 EA 32 32.5 69 5 2,354 39,100 (A) 0.5

0. 040-. 010 5 BA 32 36.5 39 5 2,349 44,500 (A) 0.9

5 0. 040. 010 6 AN/MA-30/70 0432 010 32.0 69 2,398 44,100 (A) 0.5 7 AN/EA/70 32 36.0 54 5 2,331 43, 300 (A) 0.5

0. 040-. 010 8 MA/sP-50/50 32 40.0 +.35 5 2,499 48, 200 (A) 1.0

'Aclalc.acetonelalcohol.

MMA-methyl methacrylate. MA-methyl acrylate. EA-ethyl acrylate. BA-butyl aerylate. AN-acrylonitrile. SIP-styrene polyester (styrene/ethylene glycol maleate-30/70). (A) Luperco ATC (50/50 mixture of benzoyl peroxide and tricresyl phosphate).

In Table 2, data are given which compare the persolventless powder and a powder of the invention of formance in cal. .30 cartrldges of a standard double base comparable potential. The two powders had the followpowder and another serles of powders of the lnventlon of i compositions; comparable potential. The powders had the following formulations Standard Invention Standard Iuvenflm 'Nitrocellulose(13.25% N) 20.0% 260 Ntglrolgl eerzini t 30.g%. Nitrocellulose 15.25 N) 81.957 34.0 Y 3 Nitroglyoerin 15.0%? 50.0%. Nlmguamdme- 340% Diphenyhmine 015% olvent 15 parts, Acetone] 15.0% (Polymeriz- Ethyl Centra1ite Alcohol 70/30. able-contains Barium Nitrate" 1.40% Potassium Nitrate- 0.75% Solvent 57tpartlsAlAcle-1 15b(1Polym%rizaone C0 10 8-0011 3.1118 150/56 0.549%) The standard powder was prepared by the technlques previously described. The powder of the invention was pre- The powders were prepared by the same processes used pared y the Procfiss used in Producing the Powders of in producing the powders of Examples 1-8. EXamples 119.

Table 2 Cut Charge Mean Mean Example Solvent GrainDia., Weight Air No. Veloc- Pres- Catalyst,

Pin Die. (gn) Space Shots ity, sure, percent ft./sec. p.s.i.

Standard Ao/alo 16 39.0 +.46 5 2,585 53,900

0053-.015 9 EMA 16 45.0 14 3 2,161 45,500 (A) 1.0

0.040.010 10 MMA 16 51.0 13 5 2,716 52,800 (A) 1.0

0.040 010 11 EMA 16 49.0 +.11 5 2,635 61,800 (4)1.0

0.040.010 12 MA 16 36.5 51 5 2,660 52,500 (A) 0.5

0.040.010 13 EA 16 37.0 +.51 5 2,026 48,800 (A) 0.5

0.040.010 14 AN/MA-35/70 16 39.0 +.36 5 2,679 55,900 (A) 0.5

0.040.010 15 AN/EA30/70 16 41.5 +.30 5 2,685 55,900 (A) 0.5

0.040.010 16 MMA 16 50.0 +.03 5 2,563 51,300 (A) 1.0

0.040.010 17 EMA 16 48.5 +.02 5 2,580 52,300 (A) 1.0

0.040.010 1s MA/SP-/50 16 45.0 14 6 2,305 57,200 (A) 1.0

0.040.010 10 EMA 16 49.0 10 5 2,616 53,300 (B) 1.0

Ac/elc.-aeetonelalc0h01.

EMA-ethyl methacrylate.

MMA-methyl methacrylate.

MA-methyl acrylate.

EA-ethy1 acrylate.

AN-acrylonltrlle.

SPstyrene polyester (styrene/ethylene gylcol lnaleate-30/70).

(A) Luperco ATO (50/50 mixture of benzoyl peroxide and trlcresyl phosphate). (B) Azo-bis-isobutyronitrile.

Nitrocellulose (13.25% N),

percent Diphenylaminc, percent. Ethyl eentralite, percent.... Dibutyl phthalate, percent.. Dinitrotoluene, percent. Ethyl methacrylate, percent Ethyl acrylate, percent Acryonitrile, percent Styrene/ethylene glycol maleate30/70, percent Die size, 7 perl Pin Mixing time, hours 4 2 2 2 2 Pressing pressure, pounds--. 1,500 500 400 200 600 Curing time, hours 8 8 8 8 Drying time, hours.... 240 a German Test, Mins 90+ 90 90+ 90+ Determ. Heat of Explosiom. 720 744 807 914 9,78 Measurements:

L (Grain length) 1.326 1. 305 1. 311 1. 312 D (Grain diameter)...-. .5320 .5269 .5252 .5052 .5083 d (Perforation diameter). 0566 0573 0640 0596 0623 We (Outer web) .0034 .0822 0777 0814 0654 Wi (Inner web) 0878 0953 0889 0818 0953 Wa (Average web) 0906 0888 .0833 0816 0808 Closed Bomb Tests:

Relative Quiekness 100.0 73. 58 91.36 129. 39 167. 26 Relative Force 100. 103. 47 109.13 122.47 118.13

Table Stand- Ex- Ex- Ex- Ex- Formulas ard ample ample ample ample Nitroglycerin, percent 15. 0 50.0 50.0 50. 0 50.0 Nitrocellulose, percent. 81. 95 34. 0 34. 0 34.0 34.0 Diphenylamine, pereent.. 0.6 Ethyl centralite, perecnt-.- 1. 0 1. 0 1. 0 1. 0 Potassium nitrate, percent.. 0 75 Barium nitrate, percent 1. 40 Graphite, percent. 0. 3 Ethyl methacrylate, percent 15.0 Ethyl acrylate, percent 15.0 10. 5 7. 5 Acrylonitrile, percent 4. 5 Styrene/ethylene glycol maleate-/70, percent 7. 5 Die size, 7 pert 680 556 556 556 556 l? 072 065 065 065 065 Pin circle 368 319 319 310 319 Mixing time, hours 3 2 2 2 2 Pressing Pressure, pounds... 400 500 600 250 700 Curing time, hours 8 8 8 8 Drying time, hours... 240 German Test, Mins 90+ 90+ 90 90 90+ Determ. Heat of Explosion.. 983 970 1, 052 1, 147 1,-164 Measurements:

L (Grain length) 1. 322 1.322 1. 311 1. 325 D (Grain diameter) 5167 5371 5314 5120 5156 d (Perforation diameter) .0612 0591 0666 0610 0622 Wo (Outer web). .0066 0902 0793 0773 0766 Wi (Inner web) 0700 0807 0865 .0872 .0879 Wa (Average web) 0833 0894 .0829 .0822 0822 Closed Bomb Tests:

Relative Quiekness 100.0 87. 39 107. 21 127. 68 134. Relative Force 100. 0 105.01 111. 42 111.42 114. 21

Table 3 Cut Charge Mean Mean Example Solvent Grain D 1a., Weight Air No. Veloc- Pres Catalyst,

Pm Dia. (gr.) Space Shots ity, sure, percent it./sec. p.s.i.

Standard 16 56 .00 5 2,184 42,800

0. 053-. 015 20 MMA 16 40 .00 1 1, 888 34,400 (A) 1.0

' o. 053-. 015 21 MA/SP30/70 32 30 .46 5 2,061 40,600 (A) 1 o MMArnethyl methaerylate. MA-methyl acrylate. SP-styrene polyester (styrene/ethylene glycol maleate30/70). (A) Luperco ATC (50/50 mixture of benzoyl peroxide and trieresyl phosphate).

Table 4 In Tables 4 and 5, standard single and double base powders and powders prepared in accordance with the instand 20 vention were produced in cannon granulation. These pow- Formulas ard ample ample ample ample ders were tested in a du Pont type closed bomb instru- 22 23 24 25 merited to give a pressure rate trace in accordance with standard military procurement acceptance testing proce- Nitroglycerin, percent 40.0 40.0 40.0 40.0

From the foregoing examples, it will be seen that the invention comprises the substitution of certain uniquely operable monomeric polymerizable materials for the conventional volatile colloiding solvents heretofore employed by the art. The monomers themselves are volatile but, in accordance with the invention, are polymerized to a polymerization product substantially free from volatile constituents. Thus, it is possible in accordance with the invention to employ conventional mixing apparatus such as a sigma blade mixer, and conventional extrusion presses. It is possible also to employ conventional dry house equipment for the curing step of the process. However, since atmospheric oxygen exhibits an inhibiting eiiect on the polymerization reaction and extends the drying period, it is preferred to cure the green grains in either an inert gas atmosphere or else in an inert liquid. It is especially preferred to employ a curing bath of a brine solution such as aqueous sodium chloride or potassium sulfate solutions. The preferred curing baths maybe heated by conventional means such as by the use of jacketed containers or by the submersion of a waterproof electrical heating unit in the bath itself.

The length of the curing step in the process of the invention will depend on the particular monomeric material employed, upon the type and amount of polymerization catalyst, and the temperature employed, which preferably is from 20-100 C. but in all cases below the ignition point of any of the ingredients present. Generally, it has been found that curing can be effected in the order of eight hours and that drying to remove curing water from the powder requires on the average about two days. Thus, the complete processing time as compared to the conventional solvent process is considerably reduced.

The powders of the invention will always contain liquid explosive nitric ester to compensate for the cooling effect of the polymerized solvent which remains in the composition. Thus, all of the powders of the invention are of the As illustrated in Examples 20 and 21 in Table 3, nonaromatic crystalline high explosives, such as nitroguanidine, cyclotrimethylenetriamine, pentaerythritol tetranitratc, ammonium nitrate, and the like, may be included in the composition if desired. Oxygencarrying salts such as barium nitrate, potassium nitrate, and the like may also be included. These crystalline explosives are incorporated in particulate form in an amount of from 5% to 40% by weight of the powder composition.

Conventional deterrents and stabilizers may either be added to the composition or employed as coatings as may be desired and by techniques known to the art. Such deterrents and stabilizers include diphenylamine, ethyl centralite, the alkyl phthalates such as dibutyl phthalate and resinous materials such as gasoline-insoluble pine wood resin (Vinsol).

Nitrocellulose of any desired degree of nitration may be employed. Generally, however, the nitrogen content will be greater than 11.5% with smokeless nitrocellulose, that is, nitrocellulose having a nitrogen content greater than 12.2% preferred. Nitroglycerin, because of its high potential, is the preferred liquid explosive nitric ester. However, other liquid explosive nitric esters such as ethylene glycol dinitrate, 1,2,3-butane'triol trinitrate, 1,2,4- butanetriol trinitrate, Z-(hydroxymethyl)-2-methyl-1,3- propanediol trinitrate, pentaerythritol trinitrate, dinitroglycerin, and the like may be employed if desired.

As previously indicated, the polymerizable solvent will be selected from the lower alkyl esters and the nitriles of acrylic and methacrylic acids. Other polymerizable materials either do not exert the necessary solvent action on nitrocellulose or else do not polymerize completely at the low temperatures which are necessary in the presence of such explosive materials as nitroglycerin, nitrocellulose and crystalline explosive. Methyl methacrylate and ethyl methacrylate are the preferred monomeric solvents. Mixtures of any of the operable monomers may also be employed. The operable monomers may also be partially polymerized prior to admixture with the remaining ingredients of the powder composition although care must be taken that the mixture does not become too viscous and that the solvent action of the materials is not inordinately atfeced. Styrene by itself is a poor solvent fornitrocellulose and therefore is not operable per se. Styrene polyesters, although they exhibit excellent curing characteristics at low temperatures, are also inoperable by themselves. However, as illustrated by the examples, excellent compositions can be obtained when styrene polyesters such as styrene/ ethylene glycol maleate are employed in admixture with one or more of the operable acrylic esters or nitriles such as acrylonitrile or methacrylonitrile.

Any of the known polymerization catalysts for vinyl type materials may be employed to catalyze the polymertricresyl phosphate, lauroyl peroxide, methyl ethyl ketone peroxide, tertiary butyl hydroperoxide, di-tert-butyl diterephthalate, and tert-butyl perbenzoate and mixtures thereof. Preferably, the catalysts will be employed in amounts ranging between 0.5% and 2.5% based on the content and type of monomer.

Furthermore, it will be appreciated that in formulation of the powders herein given, there is some loss of monomer solvent by the time the powders are completely processed. This, of course, can be compensated for by adding additional monomer at the time of mixing.

In accordance with the invention herein described and illustrated, the desired solvent process may be employed in the manufacture of smokeless powder without the usual ballistic abberations resulting from the presence of residual volatile solvent. Thus, large grains of smokeless powder for use in rockets and JATOs may be prepared by extrusion of smokeless powder compositions plasticized with polymerizable solvent in accordance with the invention and a casting process need not be employed for grains having large web. Where the smokeless powder in accordance with the invention is employed as base grain in casting techniques, the problem of solvent migration is likewise removed.

izable material. Such catalysts include benzoyl peroxide, T

Additionally, large web powders and stick powders that are normally made by the solventless process, because of excessive drying time when using the conventional solvent process, can now be made in accordance with this invention by using conventional solvent type equipment and techniques associated with such equiment.

Since modifications of the invention will be apparent to those skilled in the art, it is intended that the scope f the invention be limited only by the appended claims.

What I claim and desire to protect by Letters Patent is:

l. A process for manufacturing smokeless powder which comprises forming a uniform doughy mass consisting essentially of from 15 to 50% of nitrocellulose, from 15 to 60% of liquid explosive nitric ester and from 5 to 30% of at least one catalyzed liquid polymerizable material selected from the group consisting of the nitriles of acrylic and methacrylic acids and a styrene polyester and mixtures thereof with lower alkyl acrylates and methacrylates, extruding the mass and cutting into the desired granulation, and curing the grains at a temperature of from about 20 C. C. and below the ignition point of any of the ingredients to form a polymerization product substantially free from volatile constituents.

2. A process according to claim 1 in which the liquid explosive nitric ester is nitroglycerin.

3. A process according to claim 1 in which the grains are cured in an inert liquid bath.

4. A process for manufacturing smokeless powder which comprises forming a uniform doughy mass containing from 15 to 50% of nitrocellulose, from 15 to 60% of liquid explosive nitric ester, from 5 to 40% of particulate crystalline high explosive, and from 5 to 30% of at least one catalyzed liquid polymerizable material of the group consisting of the methyl, ethyl, propyl, butyl and isobutyl esters and the nitriles of acrylic and methacrylic acids,

extruding the mass and cutting into the desired granulation, and curing the grains at a temperature of above 20 C. and below the ignition point of any of the ingredients to .form a polymerization product substantially free from volatile constituents.

5. A process according to claim 4 in which-the liquid explosive nitric ester is nitroglycerin.

6. A process according to claim 4 in which the polymerizable materal is methyl methacrylate.

7. A process according to claim 4 in which the polymerizable material is ethyl methacrylate.

8. A process according to claim 4 in which the grains are cured at a temperature of from 20-l00 C.

9. A process according to claim 4 in which the grains are cured in an inert liquid bath.

10. As a new article of manufacture, a granulated smokeless powder substantially'free of volatile constituents consisting essentially of from 15 to 50% nitrocellulose, from 15 to 60% liquid explosive nitric ester, and from 5 to 30% of at least one polymerized material selected from the group consisting of the nitriles of acrylic and methacrylic acids and a styrene polyester and mixtures thereof with lower alkyl acrylates and methacrylates.

11. As a new article of manufacture, a granulated smokeless powder substantially free of volatile constituents and comprising from 15 to 50% nitrocellulose, from 15 to 60% liquid explosive nitric ester, from 5 to 40% particulate crystalline high explosive, and from 5 to 30% of at least One polymerized material of the group consisting of the methyl, ethyl, propyl, butyl and isobutyl esters and the nitriles of acrylic and methacrylic acids.

No references cited. 

1. A PROCESS FOR MANUFACTURING SMOKELESS POWDER WHICH COMPRISES FORMING A UNIFORM DOUGHY MASS CONSISTING ESSENTIALLY OF FROM 15 TO 50% OF NITROCELLULOSE, FROM 15 TO 60% OF LIQUID EXPLOSIVE NITRIC ESTER AND FROM 5 TO 30% OF AT LEAST ONE CATALYZED LIQUID POLYMERIZABLE MATERIAL SELECTED FROM THE GROUP CONSISTING OF THE NITRALES OF ACRYLIC AND METHACRYLIC ACIDS AND A STYRENE POLYESTER AND MIXTURES THEREOF WITH LOWER ALKYL ACRYLATES AND METHACRYLATES, EXTRUDING THE MASS AND CUTTING INTO THE DESIRED GRANULATION, AND CURING THE GRAINS AT A TEMPERATURE OF FROM ABOUT 20*C.-100*C. AND BELOW THE IGNITION POINT OF ANY OF THE INGREDIENTS TO FORM A POLYMERIZATION PRODUCT SUBSTANTIALLY FREE FROM VOLATILE CONSTITUENTS.
 10. AS A NEW ARTICLE OF MANUFACTURE, A GRANULATED SMOKELESS POWDER SUBSTANTIALLY FREE OF VOLATILE CONSTITUENTS CONSISTING ESSENTIALLY OF FROM 15 TO 50% NITROCELLULOSE, FROM 15 TO 60% LIQUID EXPLOSIVE NITRIC ESTER, AND FROM 5 TO 30% OF AT LEAST ONE POLYMERIZED MATERIAL SELECTED FROM THE GROUP CONSISTING OF THE NITRILES OF ACRYLIC AND METHACRYLIC ACIDS AND A STYRENE POLYESTER AND MIXTURES THEREOF WITH LOWER ALKYL ACRYLATES AND METHACRYLATES. 